Weather Proof Walls

Pebble-Dash

The term is used to describe external rendering where smooth pebbles (10-12mm Pea Gravel) are thrown or “dashed” onto a receiver coat, i.e. the topcoat of render, before it cures, so that they stick and embed themselves into it.

The pebbles are lightly and evenly tamped into the receiver coat with a plastic or wooden float. The idea behind it was purely aesthetic, to provide an ‘attractive’ weathering surface and was specified extensively in the 1930’s.

A lot of home owners attempted to change the appearance by over-painting or applying Tyrolean over the top. It is less desirable and not called for much these days, unless of course it is for conservation and restoration purposes, returning the building to its original state.

It is a traditional treatment that can be problematic for older buildings. It is extremely porous, assuming no waterproofing additive is present. It absorbs rain water like a sponge and feeds penetrating damp, thus resulting in long term damage and erosion to the structure. The great thing, however, is that left untreated with high porosity it tends to dry faster when saturated after a rainstorm.

The net result of our experience is the pebbles fall off , it cracks, and is never guaranteed to stay on the wall for long, particularly in today’s climate and atmospheric conditions. It cracks easily and is generally difficult to repair without it being very obvious that a repair has been made to the wall. It is a source of continuous maintenance once the material begins to deteriorate; it should be good for 10 years depending on the correct mix and application, location and environmental context.

With today’s high levels of atmospheric pollution it has become virtually obsolete, however, with the intended atmospheric/environmental clean up plans over the next twenty years and future product innovation perhaps we shall see a pebble-dash renaissance, who knows!

Spar-dash

Spar-dash is a close relation. It uses jagged chippings that tend to interlock and adhere to the render in the same way  as pebble-dash but better, thus lasting longer. There are various forms of spar, some of which use ordinary stone, which can look a bit dull, and others where the chippings are chosen for their particular colour, such as with “Canterbury” or “Dolomite”.

A much wider selection of natural and man made materials are available today including coloured glass and resins which can look stunning.

Otherwise, neither spar nor pebble-dash requires very much maintenance assuming it has been applied correctly and substrates have been prepared properly which is always the key with any surface application; sweeping up the pebbles can be an ongoing irritation that teaches people to grow to dislike their own home.

There are many more alternatives available on the market today. Advanced coating technology that brings better vapour permeability, coatings that both resist and shed surface rain water, protect from enhanced ultra violet light penetration and enhance the decorative finish and colour fastness which also contain anti-fungicides to eliminate the potential for fungal and vegetative surface growth.

One product we use actually draws out the colours of the pebbles and spar chippings, providing more visual impact and a longer lasting impression through light refraction and the natural colours inherent in the material.

Such is the development of this new wall sealant treatment,  it is vapour permeable and thus maintains the integrity of the building by enabling the render to breathe properly and more naturally, without it looking like the surface is shiny or glossy like so many other treatments do.

In our opinion this suite of products is absolutely ideal for treating natural brick and natural stone and spar chipped traditional renders, which makes them more weather and water resistant at the same time.

One of the questions we get asked a lot is; can we render on top of pebble-dash?

This can be problematic; it very much depends on the quality and integrity of the base render, e.g. is it frost damaged; is it hollow sounding when you tap it; has it been treated with waterproofing additives? Remember what ever you decide to leave on the wall may affect what ever you decide to put on the top.

Most professional firms would avoid recommending over-coating render or pebble dash of this sort, as it may have absorbed high traces of pollutants which will remain and may continue to corrode any new top coat that is applied. Any guarantee given is almost certain to qualify against defects occurring as a result of contaminated sub-strate, thus ‘rendering’ the guarantee ineffective.

The cost of trying to make good existing render can lead to false economy.  It would serve best to remove and replace with new to minimise future risk of failure.

It’s not all bad news!  This could also provide an ideal opportunity to think of insulating the walls before the property is re-rendered, thus improving the energy efficiency of the home and the U value of the wall construction. This way, through lower energy bills, moving the whole exercise from being an ongoing maintenance cost to an investment in the home that reaps cash and comfort benefits for years to come.

Other benefits are: As render is removed the walls can be better inspected, leaking cracks repaired and friable crumbling bricks replaced. This will allow better levels to be set for the new render and will provide a flatter and more even finish for the finish coat to be applied, producing a better job in the long run.

Rough-cast

Rough Cast uses a slurry of stones made of variable sized aggregate, basically sharp aggregate and cement mixed and dashed onto the base coat of the rendered surface when it’s dry. It is usually a much more aggressive texture and produces the appearance of a Sheep’s woolly coat to the property. It looks and feels different, its success depends on the right building design, location and context for it to work visually.

Roughcast is generally painted and brings forward all the attendent problems that none breathable wall coatings engender. It is generally made of a very strong cement sand and aggregate mix and is notoriously difficult to remove without seriously damaging the bricks underneath. Again not used much these days and inadvisable to remove uless badly degragated.

Tyrolean

Tyrolean is a brand name originating from a traditional alpine building process. Tyrolean can be achieved with all sorts of materials but externally is now referred to a proprietory pre mixed material. It is approximately 3-4mm in thickness and can be obtained self coloured.

It provides a thin coat finish used widely throughout the industry in the 70’s and 80’s. The success of the product very much depends on the competence of the applicator, proper preparation and the surface integrity it is applied to.

The brand product is machine applied and takes real patience and skill not to create distinguishable day/cold joints and noticeable overloading of the product giving the appearance of being uneven and lumpy..

Our experience is that we have come across many properties failing with this product and equally there are many reasons for this. It is never recommended by us; it is highly porous and therefore is susceptible to frosting and flaking.

It produces a thin coat finish that when obsolete produces a very suspect substrate on which to apply further coatings. Because it is thin it is very difficult to remove once applied. It bubbles and blows off the substrate over time but it is a very cheap way to coat walls and is often painted propagating further internal damp and mould growth problems.

Painting

Painting any textured surface is time consuming and takes plenty of patience and material to fill in all the gaps but it does brighten up an otherwise lack lustre finish. However, once painted it can’t really be re-rendered without taking the surface back to the original wall surface and to establish a good base and key for the next application.

Painting anything is possible but when it comes to buildings that need to breathe choice of paint is crucial. Remember, once the wrong paint is applied it cannot be removed easily and can lead to all sorts of problems  from internal mould, increased damp, condensation, high energy consumption through moisture retention, and more seriously over time the accelerated deterioration of the structural elements of the building.